1. Field of the Invention
The present invention relates to laser welding techniques by which a layered base material composed of two or more layers is integrally bonded by welding to form a laminated bonded material, and in particular, relates to laser welding techniques by which three or more plates are stacked in a laminated state so as to be integrally bonded, although the scope of the invention is not limited thereto.
2. Description of the Related Art
YAG laser welding has characteristics described below and has been widely employed in automatic welding such as for automobiles.
(1) Convergent laser light can be produced and low distortion and high speed welding are possible.
(2) Since the laser light absorption factor thereof in a metal material is several times that of a CO2 laser beam, high efficiency welding is possible. Furthermore, since the wavelength is one-tenth that of a CO2 laser beam, it is not significantly influenced by plasma generated during welding.
(3) Since laser light can be transmitted by means of a flexible optical fiber, manipulation is easy and a multi-jointed robot can be utilized. Furthermore, it can be transmitted to a place distanced up to about 100 m distant therefrom.
(4) Since in laser light, time sharing and power sharing are possible, by using it at a plurality of work stations, a high utilization efficiency can be obtained.
However, there are problems in the welding in which a YAG laser beam alone is used, as described below.
(1) In a YAG laser beam, a light beam is focused to increase energy concentration, thereby executing welding. However, since the focused light spot diameter is 0.3 to 1 mm, which is very small, in lamination welding, the bonding interface width of a through bead from an upper plate to a lower plate is narrow, and thus the bonding strength is not high. In the case where lamination welding of three or more layers is implemented, there are cases in which welding is performed from one side (for example, from a front side) and where welding is performed from both sides, one surface each time, while the process speed is reduced. In either case, a long processing time is required, and the lowest plate tends to be deformed due to heat distortion during welding, whereby satisfactory welding cannot be obtained.
(2) Since the initial cost of a YAG laser welding device is high, in the case where plural pieces of device are introduced, such as in an automobile production line, the cost of the device is enormous.
It is an object of the present invention to provide a lamination welding, using a laser beam, in which there is little distortion and the bonding strength is high.
A laser welding device according to the invention is characterized by comprising a first laser beam emitting head (9) directed to a layered base material (21) composed of two or more layers in a superimposed direction; a first skirting roller (8) rotatably supported by means of a first supporting member (4) on which the first laser beam emitting head is fixed and provided with a peripheral surface which protrudes more at a base material side than a base material opposing end of the first laser beam emitting head; a second laser beam emitting head (19) directed to the layered base material from the opposite side of the first laser beam emitting head in the superimposed direction; a second skirting roller (18) rotatably supported by means of a second supporting member (14) on which the second laser beam emitting head is fixed and provided with a peripheral surface which protrudes more in a base material side than a base material opposing end of the second laser beam emitting head; and a first pressing means (6) for pressing the first supporting member (4) with respect to a supporting base holder (2) in the superimposed direction (z).
To facilitate understanding, reference numerals shown in the accompanying drawings which denote corresponding or equivalent components in the embodiment described below are appended in parenthesis for reference. The following are described similarly thereto.
In the above-described device, the first pressing means (6) presses the first supporting member (4) in the superimposed direction (z) of the layered base material, and thus the first skirting roller (8) supported by means of the first supporting member (4) abuts the base material (21) to press the base material, whereby the base material (21) is pressed to abut the second skirting roller (18). That is, the base material (21) is pressed and sandwiched by the first skirting roller (8) and the second skirting roller (18). The first laser beam emitting head (9) and the second laser beam emitting head (19) emit laser beams so that fusion pools 32 and 33 going across a layered bonding portion are created as shown in FIG. 5A or FIG. 5B. At this time since the base material (21) is pressed by the first skirting roller (8) and the second skirting roller (18), adhesion of the layered bonding portion is excellent, and the fusion pools of the upper and lower two materials of the layered bonding portion are united, whereby welding with a high bonding strength can be achieved. Furthermore, since both the front side and the back side of the layered base material are supported by means of the skirting rollers, deformation of the respective layered plates is inhibited, and a lamination with an excellent finished form can be obtained.
In a preferred embodiment, the laser welding device according to the present invention further comprises a first head gap adjustment mechanism (7) for adjusting the position of a first roller supporting member (34) which rotatably supports the first skirting roller (8) in the superimposed direction (z) with respect to the first supporting member (4) and a second head gap adjustment mechanism (17) for adjusting the position of a second roller supporting member (35) which rotatably supports the second skirting roller (18) in the superimposed direction with respect to the second supporting member (14).
This enables the distances of the first and second laser beam emitting heads (9, 19), with respect to the layered base material (21) (laser focus position in the thickness direction of the base material), to be simply adjusted by means of the first and second head gap adjustment mechanisms (7, 17).
In a preferred embodiment, the laser welding device according to the present invention further comprises a second pressing means (16) for pressing the second supporting member (14) with respect to the base holder (3) in the superimposed direction (z).
Since this enables the respective emitting heads (9, 19) to approach the base material (21) from both the front side and the back side of the base material (21) at the same time, the relative positioning of both the emitting heads (9, 19) and the base material (21) in the superimposed direction (z) can be easily executed.
Furthermore, in a preferred embodiment of the laser welding device according to the present invention, the first supporting member (4) is supported by means of one end (2) of a U-shaped-supporting base holder (1) and the second supporting member (14) is supported by means of the other end thereof (3). With this structure, by operating the supporting base holder (1) to move both emitting heads (9, 19) at the same time, positioning with respect to the base material (21) can be executed.
Moreover, in a preferred embodiment of the laser welding device according to the present invention (FIG. 2), a cable (20) which transmits a laser beam to the second laser beam emitting head (19), an optical system (19a) which makes the laser beam emitted from the cable parallel, and one end of an expansion cylinder (23) are supported by means of a supporting base holder (22) which supports the first supporting member (4), and the direction of the laser beam is changed 90 degrees by means of a mirror (24) at the other end of the expansion cylinder and is further changed 90 degrees by means of another mirror (26) so that the laser beam is guided to a convergence optical system (19b) of the second laser beam emitting head (19). With this structure, since two cables (10, 20) which transmit laser beams to the first and second laser beam emitting heads (9, 19) exist at the front side in which the first laser beam emitting head (9) opposes, it is not necessary to dispose a cable at the back side.
Furthermore, in a preferred embodiment of the laser welding device according to the present invention (FIG. 3), a laser beam emitted from a laser beam transmitting cable (10) is made substantially parallel by means of an optical system (9a), the direction of a part thereof is changed 90 degrees by means of a half mirror (27) and is further changed 90 degrees by means of another mirror (29) so that the laser beam is guided to a convergence optical system (9b) of the first laser beam emitting head (9), and the direction of the laser beam which has passed through the half mirror (27) is changed 90 degrees by means of a mirror (24) and is further changed 90 degrees by means of another mirror (26) so that the laser beam is guided to a convergence optical system (19b) of the second laser beam emitting head (19). Since this enables one laser beam transmitting cable (10) to supply a laser beam to the first and second laser beam emitting heads (9, 19), cable disposition becomes simple.
In a preferred embodiment of the laser welding device according to the present invention (FIG. 4), a laser beam emitted from a laser beam transmitting cable (10) is divided into two by means of a beam splitter (30), the direction of one laser beam is changed 90 degrees by means of a mirror (31) and is further changed 90 degrees by another mirror (29) so that the laser beam is guided to an convergence optical system (9b) of the first laser beam emitting head (9), and the direction of the other laser beam is changed 90 degrees by means of a mirror (24) and is further changed 90 degrees by another mirror (26) so that the laser beam is guided to a convergence optical system (19b) of the second laser beam emitting head (19). Since this enables one laser beam transmitting cable (10) to supply a laser beam to the first and second laser beam emitting heads (9, 19), cable disposition becomes simple.
It is preferred that the laser beam used in the laser welding device according to the present invention be a YAG laser beam. This enables efficient welding. Furthermore, it is possible for a welding head to be placed at a distance from the laser light source, for example, supported by a robot arm, and connected to the laser light source by an optical fiber cable, whereby operability of the welding head is greatly improved.
A laser welding method according to the present invention is characterized by comprising the steps of sandwiching a layered base material (21) composed of two or more layers by means of skirting rollers (8, 18) and pressing the base material in a superimposed direction (z) and emitting a laser beam from a front side and a back side of the layered base material (21) in the superimposed direction (z) by means of a first laser beam emitting head (9) and a second laser beam emitting head (19) so that the front side and the back side of the base material (21a, 21c) are melted up to a layered bonding portion.
This enables interactions and effects of the present invention to be similarly obtained.
In the laser welding methods according to the present invention, it is preferred that, in the case in which fusion depths from the front side and the back side are not superimposed in the superimposed direction (z) (FIGS. 5A, 5C), target positions of the first laser beam emitting head (9) and the second laser beam emitting head (19) be made substantially the same (FIGS. 5A, 5C).
Furthermore, in the laser welding process according to the present invention, it is preferred that, in the case in which the fusion depths from the front side and the back side are superimposed in the superimposed direction (z), the target positions of the first laser beam emitting head (9) and the second laser beam emitting head (19) be shifted in a direction (x) which is perpendicular to the superimposed direction (z) so that fusion positions from the front side and the back side are not superimposed at the same time (FIGS. 5B, 5D).